endpoint for adding logs

[JuliaGlocka]

• [ ] input json schema would be: app_name, timestamp, app_version, level, message
• [ ] describe the endpoint /log in flask
• [ ] use flask-expects-json plugin to validate the request json payload (refer to: https://stackoverflow.com/questions/63773044/python-flask-json-schema-validation)
• [ ] if response is wrong return error message, this lib must give some error messages for sure
• [ ] record log to mongodb, each app_name should be in separate collection. remove app_name from json before saving results to mongo